A transistor basically includes a source, a drain, a channel therebetween and a gate. Conduction selectively occurs or is prevented within the channel depending on a voltage applied to the gate, as is well known. Carrier mobility is a principal factor in maintaining adequate performance of the transistor, which affects the amount current or charge flowing in the channel under control of the voltage applied to the gate.
A transistor having low carrier mobility will reduce not only the switching speed but also reduce the difference between “on” resistance and “off” resistance. Therefore, improvements in carrier mobility of the channel continue to be sought.